Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $101.47   4.214%   $105.7459   $105.75   $105.75   $105.70  
  Purchase #2 $219.58   10.652%   $242.9697   $242.97   $242.95   $243.00  
  Purchase #3 $245.93   8.636%   $267.1685   $267.17   $267.15   $267.20  
  Purchase #4 $73.65   10.408%   $81.3155   $81.32   $81.30   $81.30  
  Purchase #5 $96.26   7.734%   $103.7047   $103.70   $103.70   $103.70  
  Purchase #6 $62.49   3.121%   $64.4403   $64.44   $64.45   $64.40  
  Purchase #7 $184.74   9.761%   $202.7725   $202.77   $202.75   $202.80  
  7 purchase totals = $984.12       $1,068.1171   $1,068.12   $1,068.05   $1,068.10